Process for the production of a PGM-enriched alloy

ABSTRACT

Processes for the production of platinum group metal (PGM)-enriched alloys are described. The PGM enriched-alloys can have 0 to 60 wt.-% of iron and 20 to 99 wt.-% of one or more PGMs selected from the group consisting of platinum, palladium and rhodium. The described processes exhibit remarkably low PGM losses during production of PGM-enriched alloys therefore yield alloys having considerably high PGM levels.

The invention relates to a pyrometallurgical converting process for theproduction of a PGM-enriched alloy and to the PGM-enriched alloy itself.

The abbreviation “PGM” used herein means platinum group metal.

In general, the enrichment of PGMs by means of pyrometallurgicalconverting is well-known, see, for example, S. D. MCCULLOUGH,Pyrometallurgical iron removal from a PGM-containing alloy, ThirdInternational Platinum Conference ‘Platinum in Transformation’, TheSouthern African Institute of Mining and Metallurgy, 2008, pages 1-8.

The invention is a pyrometallurgical converting process improved interms of yielding a PGM-enriched alloy having a considerable high PGMlevel and exhibiting a remarkably low PGM loss into slag formed asby-product of the pyrometallurgical converting process.

The process of the invention is a process for the production of aPGM-enriched alloy comprising 0 to 60 wt.-% (weight-%) of iron and 20 to99 wt.-% of one or more PGMs selected from the group consisting ofplatinum, palladium and rhodium. The process comprises the steps:

-   (1) providing a PGM collector alloy comprising 30 to 95 wt.-% of    iron, less than 1 wt.-% of sulfur and 2 to 15 wt.-% of one or more    PGMs selected from the group consisting of platinum, palladium and    rhodium,-   (2) providing a copper- and sulfur-free material capable of forming    a slag-like composition when molten, wherein the molten slag-like    composition comprises 40 to 90 wt.-% of magnesium oxide and/or    calcium oxide and 10 to 60 wt.-% of silicon dioxide,-   (3) melting the PGM collector alloy and the material capable of    forming a slag-like composition when molten in a weight ratio of    1:0.2 to 1 within a converter until a multi- or two-phase system of    a lower high-density molten mass comprising the molten PGM collector    alloy and one or more upper low-density molten masses comprising the    molten slag-like composition has formed,-   (4) contacting an oxidizing gas comprising 0 to 80 vol.-% (volume-%)    of inert gas and 20 to 100 vol.-% of oxygen with the lower    high-density molten mass obtained in step (3) until it has been    converted into a lower high-density molten mass of the PGM-enriched    alloy (i.e. a lower high-density molten mass of the composition of    the PGM-enriched alloy),-   (5) separating an upper low-density molten slag formed in the course    of step (4) from the lower high-density molten mass of the    PGM-enriched alloy making use of the difference in density,-   (6) letting the molten masses separated from one another cool down    and solidify, and-   (7) collecting the solidified PGM-enriched alloy.

“0 wt.-%” or “0 vol.-%” appears several times in the description and theclaims; it means that the respective component is not present or, ifpresent, it is at best present in a proportion of no more than at atechnically inevitable impurity level.

The process of the invention is a process for the production of aPGM-enriched alloy comprising 0 to 60 wt.-% of iron and 20 to 99 wt.-%of one or more PGMs selected from the group consisting of platinum,palladium and rhodium. It is preferred that the PGM-enriched alloyproduced by the process of the invention comprises 0 to 45 wt.-% of ironand 30 to 99 wt.-% of one or more of said PGMs, in particular 0 to 20wt.-% of iron and 40 to 90 wt.-% of one or more of said PGMs. ThePGM-enriched alloy made by the process of the invention may alsocomprise 0 to 60 wt.-% of nickel and 0 to 5 wt.-% of copper. Examples ofother elements (elements other than iron, nickel, copper, platinum,palladium and rhodium) which may be comprised by the PGM-enriched alloymade by the process of the invention include, in particular, silver,gold, aluminum, calcium and silicon. The PGM-enriched alloy made by theprocess of the invention may comprise one or more of said other elementsin a total proportion of up to 10 wt.-%. Hence, the PGM-enriched alloymade by the process of the invention may comprise or consist of:

-   0 to 60 wt.-%, preferably 0 to 45 wt.-%, in particular 0 to 20 wt.-%    of iron,-   20 to 99 wt.-%, preferably 30 to 99 wt.-%, in particular 40 to 90    wt.-% of one or more PGMs selected from the group consisting of    platinum, palladium and rhodium,-   0 to 60 wt.-% of nickel,-   0 to 5 wt.-% of copper, and-   0 to 10 wt.-%, preferably 0 to 6 wt.-%, in particular 0 to 3 wt.-%    of one or more other elements, in particular, one or more other    elements selected from the group consisting of silver, gold,    aluminum, calcium and silicon.

In an embodiment, the PGM-enriched alloy made by the process of theinvention comprises or consists of 0 to 20 wt.-% of iron, 40 to 90 wt.-%of one or more PGMs selected from the group consisting of platinum,palladium and rhodium, 0 to 60 wt.-% of nickel, 0 to 5 wt.-% of copperand 0 to 3 wt.-% of one or more other elements, in particular, one ormore other elements selected from the group consisting of silver, gold,aluminum, calcium and silicon.

In step (1) of the process of the invention a PGM collector alloy isprovided.

PGM collector alloys are well-known to the person skilled in the art;they may typically be formed during pyrometallurgic recycling ofappropriate PGM containing waste material like, for example, PGMcontaining waste catalysts, for example, used automotive exhaustcatalysts. In the course of such pyrometallurgic recycling the PGMs areseparated by smelting the PGM containing waste material, for example,ceramic supports having a PGM containing washcoat (like used automotiveexhaust catalysts) together with a collector metal like, for example,iron in an oven, a so-called smelter. The PGMs form a PGM collectoralloy with the collector metal, which is separated from slag formed asby-product during smelting.

The PGM collector alloy provided in step (1) comprises 30 to 95 wt.-% ofiron; less than 1 wt.-% or, in particular, even 0 wt.-% of sulfur; and 2to 15 wt.-% of one or more PGMs selected from the group consisting ofplatinum, palladium and rhodium.

In an embodiment, the PGM collector alloy may comprise 40 to 70 wt.-% ofiron; 0 to 20 wt.-% of nickel; less than 1 wt.-% or, in particular, even0 wt.-% of sulfur; and 5 to 15 wt.-% of one or more of said PGMs. It ispreferred that the PGM collector alloy comprises no more than 4 wt.-%,in particular ≤1 wt.-% of copper. Examples of other elements (elementsother than iron, nickel, sulfur, copper, platinum, palladium andrhodium) which may be comprised by the PGM collector alloy includesilver, gold, aluminum, calcium, silicon, phosphorus, titanium,chromium, manganese, molybdenum and vanadium. The PGM collector alloymay comprise one or more of said other elements in a total proportion ofup to 30 wt.-%. Hence, the PGM collector alloy may comprise or consistof:

-   30 to 95 wt.-%, in particular 40 to 70 wt.-% of iron,-   0 to 20 wt.-%, in particular 0 to 15 wt.-% of nickel,-   2 to 15 wt.-%, in particular 5 to 15 wt.-% of one or more PGMs    selected from the group consisting of platinum, palladium and    rhodium,-   less than 1 wt.-%, in particular 0 wt.-% of sulfur,-   0 to 4 wt.-%, in particular 0 to 1 wt.-% of copper, and-   0 to 30 wt.-%, in particular 0 to 20 wt.-% of one or more other    elements, in particular, one or more other elements selected from    the group consisting of silver, gold, aluminum, calcium, silicon,    phosphorus, titanium, chromium, manganese, molybdenum and vanadium.

If the PGM collector alloy comprises silicon, there may be two variants.In a first variant the silicon content of the PGM collector alloy may bein the range of 0 to 4 wt.-%, in a second variant it may be in the rangeof >4 to 15 wt.-%.

In an embodiment, the PGM collector alloy comprises or consists of 40 to70 wt.-% of iron, 0 to 15 wt.-% of nickel, 5 to 15 wt.-% of one or morePGMs selected from the group consisting of platinum, palladium andrhodium, 0 to <1 wt.-% of sulfur, 0 to 1 wt.-% of copper, 0 to 20 wt.-%of one or more other elements, in particular, one or more other elementsselected from the group consisting of silver, gold, aluminum, calcium,silicon, phosphorus, titanium, chromium, manganese, molybdenum andvanadium.

In step (2) of the process of the invention a copper- and sulfur-freematerial capable of forming a slag-like composition when molten(hereinafter also called “material capable of forming a slag-likecomposition when molten” for short) is provided.

The term “copper- and sulfur-free” used herein in the context of step(2) of the process of the invention means that the material capable offorming a slag-like composition when molten may comprise copper andsulfur, each of both however in a proportion of no more than at atechnically inevitable impurity level of, for example, less than 1000wt.-ppm.

The term “material capable of forming a slag-like composition whenmolten” used herein shall illustrate that the molten material looks andbehaves like a slag. It shall at the same time express that it is not tobe confused with the slag formed as by-product of the process of theinvention, i.e. the slag obtained after conclusion of step (4).Moreover, the material capable of forming a slag-like composition whenmolten is not necessarily identical in composition with the one or moreupper low-density molten masses formed in step (3), although it forms atleast a predominant part of the latter.

The material capable of forming a slag-like composition when molten hasa composition such that the molten slag-like composition comprises orconsists of:

-   40 to 90 wt.-% of magnesium oxide and/or calcium oxide,-   10 to 60 wt.-% of silicon dioxide,-   0 to 20 wt.-%, in particular 0 wt.-% of iron oxide (in particular    FeO),-   0 to 20 wt.-%, in particular 0 to 10 wt.-% of sodium oxide,-   0 to 20 wt.-%, in particular 0 to 10 wt.-% of boron oxide, and-   0 to 2 wt.-%, in particular 0 wt.-% of aluminum oxide.

If the silicon content of the PGM collector alloy provided in step (1)is in the range of 0 to 4 wt.-%, it is expedient that the materialcapable of forming a slag-like composition when molten has a compositionsuch that the molten slag-like composition comprises or consists of:

-   40 to 60 wt.-% of magnesium oxide and/or calcium oxide,-   40 to 60 wt.-% of silicon dioxide,-   0 to 20 wt.-%, in particular 0 wt.-% of iron oxide (in particular    FeO),-   0 to 20 wt.-%, in particular 0 to 10 wt.-% of sodium oxide,-   0 to 20 wt.-%, in particular 0 to 10 wt.-% of boron oxide, and-   0 to 2 wt.-%, in particular 0 wt.-% of aluminum oxide.

If the silicon content of the PGM collector alloy provided in step (1)is in the range of >4 to 15 wt.-%, it is expedient that the materialcapable of forming a slag-like composition when molten has a compositionsuch that the molten slag-like composition comprises or consists of:

-   60 to 90 wt.-% of magnesium oxide and/or calcium oxide,-   10 to 40 wt.-% of silicon dioxide,-   0 to 20 wt.-%, in particular 0 wt.-% of iron oxide (in particular    FeO),-   0 to 20 wt.-%, in particular 0 to 10 wt.-% of sodium oxide,-   0 to 20 wt.-%, in particular 0 to 10 wt.-% of boron oxide, and-   0 to 2 wt.-%, in particular 0 wt.-% of aluminum oxide.

In an embodiment, and apart from said wt.-% proportions of silicondioxide and magnesium oxide and/or calcium oxide, the material capableof forming a slag-like composition when molten has a composition suchthat the molten slag-like composition comprises no iron oxide, 0 to 10wt.-% of sodium oxide, 0 to 10 wt.-% of boron oxide and no aluminumoxide.

The material capable of forming a slag-like composition when molten and,as a consequence thereof, also the molten slag-like composition itselfdoes not comprise PGMs with the exception of technically inevitableimpurities. However, if the latter is present its proportion should below; preferably such proportion does not exceed, for example, 10 wt.-ppmin the material capable of forming a slag-like composition when molten.

The material capable of forming a slag-like composition when molten is acombination of substances and may comprise the afore mentioned oxides oronly said oxides, however, this is not necessarily the case. It mayinstead or additionally comprise compounds capable of forming suchoxides or oxide compositions when heated during formation of the one ormore upper low-density molten masses. To name just a few examples ofsuch type of compounds: carbonates are examples of compounds which maysplit off carbon dioxide and form the corresponding oxides when heatedand melted during formation of the one or more upper low-density moltenmasses; silicates are examples of compounds which may form thecorresponding oxides and silicon dioxide when heated and melted duringformation of the one or more upper low-density molten masses; boratesare examples of compounds which may form the corresponding oxides andboron oxide when heated and melted during formation of the one or moreupper low-density molten masses.

In step (3) of the process of the invention the PGM collector alloy andthe material capable of forming a slag-like composition when molten aremelted in a weight ratio of 1:0.2 to 1, preferably 1:0.2 to 0.8, evenmore preferably 1:0.2 to 0.6 within a converter until a multi-phasesystem of a lower high-density molten mass comprising the molten PGMcollector alloy and two or more upper low-density molten masses jointlycomprising the molten slag-like composition has formed or, in anembodiment, until a two-phase system of a lower high-density molten masscomprising the molten PGM collector alloy and an upper low-densitymolten mass comprising the molten slag-like composition has formed.

The converter is a conventional pyrometallurgical converter vessel orcrucible furnace which allows for melting the PGM collector alloy andthe material capable of forming a slag-like composition when molten. Theconverter has one or more openings at its top and it may have acylinder- or pear-like shape, for example. Its construction may be suchthat it allows for a rotating and/or rocking movement to allow supportof mixing of its contents. Preferably it is tiltable to allow forpouring out molten content thus enabling performing step (5) of theprocess of the invention. Its inner which has contact with the multi- ortwo-phase system of the lower high-density molten mass and the one ormore upper low-density molten masses is of a heat-resistant material asis conventional for pyrometallurgical converter vessels, i.e. a materialwhich withstands the high temperatures prevailing in process steps (3)and (4) and which is essentially inert towards the components of saidmulti- or two-phase system. Examples of useful heat-resistant materialsinclude silica bricks, fireclay bricks, chrome-corundum bricks, zirconmullite bricks, zircon silicate bricks, magnesia bricks and calciumaluminate bricks.

In the course of step (3), first of all, the PGM collector alloy and thematerial capable of forming a slag-like composition when molten areintroduced into the converter, either as premix or as separatecomponents. The process of the invention is a batch process and it ispreferred not to introduce the entire batch all at once and then to heatand melt the contents of the converter, but to introduce the materialsto be melted portionwise and adapted to the melting speed. Once theentire batch has melted, said multi- or two-phase system of a lowerhigh-density molten mass and the one or more upper low-density moltenmasses is obtained.

Heating of the converter contents in order to melt the latter and thusform the multi- or two-phase system means raising the temperature of theconverter contents to, for example, 1200 to 1800° C., preferably 1500 to1700° C. Such heating may be performed by various means either alone orin combination, i.e. for example plasma heating, indirect electricalheating, arc heating, inductive heating, indirect heating with burners,direct heating with one or more gas burners from the above and anycombination of said heating methods. Direct heating with gas burnerscapable of producing said high temperatures is a preferred method.Examples of useful gas burners include gas burners run with hydrogen ora hydrocarbon-based fuel gas and oxygen or nitrous oxide as oxidant.

After conclusion of step (3), i.e. once the multi- or two-phase systemhas formed, step (4) of the process of the invention is performed. Instep (4) an oxidizing gas comprising or consisting of 0 to 80 vol.-% ofinert gas and 20 to 100 vol.-% of oxygen, preferably 0 to 50 vol.-% ofinert gas and 50 to 100 vol.-% of oxygen, in particular 0 vol.-% inertgas and 100 vol.-% of oxygen (i.e. oxygen gas) is contacted with thelower high-density molten mass obtained in step (3) until the latter hasbeen converted into a lower high-density molten mass of the PGM-enrichedalloy, i.e. the PGM-enriched alloy, has formed. Any gas inert towardsthe lower high-density molten mass can be taken as the inert gas, inparticular argon and/or nitrogen. In preferred embodiments, contactbetween the oxygen or oxygen containing oxidizing gas and the lowerhigh-density molten mass can be made by passing or bubbling the gasthrough the lower high-density molten mass from the bottom of theconverter and/or by means of a gas lance the exhaust of which beingimmersed into the lower high-density molten mass. The duration of thecontact with the oxidizing gas or, in other words, the amount ofoxidizing gas employed depends on when the PGM-enriched alloy of thedesired composition has formed. In still other words, the contact withthe oxidizing gas is maintained for such period of time, until aPGM-enriched alloy with a desired composition according to any of theafore disclosed embodiments has formed; this will typically take 1 to 5hours or 2 to 4 hours, for example. The development of the compositionof the lower high-density molten mass during performance of step (4)until the PGM-enriched alloy of the desired composition has formed, canbe tracked by standard analytical techniques, for example, XRF (X-rayfluorescence) analysis. As by-product an upper low-density molten slagis formed in the course of step (4).

The contact with the oxidizing gas leads to an exothermic oxidationreaction in the course of which nonprecious elements or metals areconverted into oxides and absorbed by the one or more upper low-densitymolten masses. The oxidation process of step (4) results in depletion ofelements or metals other than the PGMs, in particular in depletion ofiron and, if present, other nonprecious elements or metals within thelower high-density molten mass or, if taking the reverse view, in PGMenrichment within the lower high-density molten mass.

After conclusion of step (4), i.e. once the PGM-enriched alloy of thedesired composition has formed, step (5) of the process of the inventionis performed. In said step (5) the upper low-density molten slag formedin step (4) is separated from the lower high-density molten mass of thePGM-enriched alloy making use of the difference in density. To this end,the content of the converter is carefully poured out making use of thewell-known decantation principle. Once the upper low-density molten slagis decanted the lower high-density molten mass of the PGM-enriched alloyis poured into suitable containers.

Steps (3) to (5) of the process of the invention constitute a sequenceof steps, in particular in direct succession. This needs to beunderstood in such sense that no further steps or at least no furtherfundamental steps are required or performed between or during said steps(3) to (5). Examples of optional non-fundamental steps are (i) theremoval of part of upper low-density molten mass in the course of step(4) or (ii) addition of PGM collector alloy and/or material capable offorming a slag-like composition when molten in the course of step (4).

After conclusion of step (5) subsequent step (6) is performed, in whichthe separated molten masses are allowed to cool down and solidify.

After solidification the solidified PGM-enriched alloy is collected instep (7). It may then be subject to further conventional refinement, forexample, electrometallurgical and/or hydrometallurgical refinement inorder to finally obtain the individual PGMs either as metal or as PGMcompound or as a solution of the latter.

It is the advantage of the process of the invention that thePGM-enriched alloy collected in step (7) is distinguished by arelatively high PGM content. This relatively high PGM content means lesseffort and less consumption of chemicals with a view to said furtherrefinement processes. It is a further remarkable advantage of theprocess of the invention that the slag formed as by-product during step(4) comprises a very low PGM content of less than 50 wt.-ppm. It is notfinally understood why, but it is believed that the 1:0.2 to 1 or 1:0.2to 0.8 or 1:0.2 to 0.6 weight ratio combination of the specificallycomposed PGM collector alloy provided in step (1) and the specificallycomposed material capable of forming a slag-like composition when moltenprovided in step (2) is key in particular with regard to the remarkablylow loss of PGMs into the slag formed as by-product during step (4) ofthe process of the invention.

The invention comprises the following embodiments:

1. A process for the production of a PGM-enriched alloy comprising 0 to60 wt.-% of iron and 20 to 99 wt.-% of one or more PGMs selected fromthe group consisting of platinum, palladium and rhodium, the processcomprising the steps:

-   (1) providing a PGM collector alloy comprising 30 to 95 wt.-% of    iron, less than 1 wt.-% of sulfur and 2 to 15 wt.-% of one or more    PGMs selected from the group consisting of platinum, palladium and    rhodium,-   (2) providing a copper- and sulfur-free material capable of forming    a slag-like composition when molten, wherein the molten slag-like    composition comprises 40 to 90 wt.-% of magnesium oxide and/or    calcium oxide and 10 to 60 wt.-% of silicon dioxide,-   (3) melting the PGM collector alloy and the material capable of    forming a slag-like composition when molten in a weight ratio of    1:0.2 to 1 within a converter until a multi- or two-phase system of    a lower high-density molten mass comprising the molten PGM collector    alloy and one or more upper low-density molten masses comprising the    molten slag-like composition has formed,-   (4) contacting an oxidizing gas comprising 0 to 80 vol.-% of inert    gas and 20 to 100 vol.-% of oxygen with the lower high-density    molten mass obtained in step (3) until it has been converted into a    lower high-density molten mass of the PGM-enriched alloy,-   (5) separating an upper low-density molten slag formed in the course    of step (4) from the lower high-density molten mass of the    PGM-enriched alloy making use of the difference in density,-   (6) letting the molten masses separated from one another cool down    and solidify, and-   (7) collecting the solidified PGM-enriched alloy.

2. The process of embodiment 1, wherein the PGM-enriched alloy comprisesor consists of 0 to 45 wt.-% of iron and 30 to 99 wt.-% of the one ormore PGMs, 0 to 60 wt.-% of nickel, 0 to 5 wt.-% of copper, and 0 to 10wt.-% of one or more other elements.

3. The process of embodiment 1, wherein the PGM-enriched alloy comprisesor consists of 0 to 20 wt.-% of iron, 40 to 90 wt.-% of the one or morePGMs, 0 to 60 wt.-% of nickel, 0 to 5 wt.-% of copper and 0 to 3 wt.-%of the one or more other elements.

4. The process of any one of the preceding embodiments, wherein the PGMcollector alloy provided in step (1) comprises 40 to 70 wt.-% of iron, 0to 20 wt.-% of nickel, less than 1 wt.-% of sulfur and 5 to 15 wt.-% ofthe one or more PGMs.

5. The process of any one of the preceding embodiments, wherein the PGMcollector alloy comprises no more than 4 wt.-% of copper.

6. The process of any one of embodiments 1 to 3, wherein the PGMcollector alloy comprises or consists of:

-   30 to 95 wt.-% of iron,-   0 to 20 wt.-% of nickel,-   0 to <1 wt.-% of sulfur,-   2 to 15 wt.-% of the one or more PGMs,-   0 to 4 wt.-% of copper, and-   0 to 30 wt.-% of one or more other elements.

7. The process of any one of embodiments 1 to 3, wherein the PGMcollector alloy comprises or consists of:

-   40 to 70 wt.-% of iron,-   0 to 15 wt.-% of nickel,-   0 to <1 wt.-% of sulfur,-   5 to 15 wt.-% of the one or more PGMs,-   0 to 1 wt.-% of copper, and-   0 to 20 wt.-% of one or more other elements.

8. The process of any one of the preceding embodiments, wherein themolten slag-like composition comprises or consists of:

-   40 to 90 wt.-% of magnesium oxide and/or calcium oxide,-   10 to 60 wt.-% of silicon dioxide,-   0 to 20 wt.-% of iron oxide,-   0 to 20 wt.-% of sodium oxide,-   0 to 20 wt.-% of boron oxide, and-   0 to 2 wt.-% of aluminum oxide.

9. The process of any one of embodiments 1 to 7, wherein the moltenslag-like composition comprises or consists of:

-   40 to 90 wt.-% of magnesium oxide and/or calcium oxide,-   10 to 60 wt.-% of silicon dioxide,-   0 wt.-% of iron oxide,-   0 to 10 wt.-% of sodium oxide,-   0 to 10 wt.-% of boron oxide, and-   0 wt.-% of aluminum oxide.

10. The process of any one of the preceding embodiments, wherein the PGMcollector alloy comprises 0 to 4 wt.-% of silicon and wherein the moltenslag-like composition comprises 40 to 60 wt.-% of magnesium oxide and/orcalcium oxide and 40 to 60 wt.-% of silicon dioxide.

11. The process of any one of embodiments 1 to 9, wherein the PGMcollector alloy comprises >4 to 15 wt.-% of silicon and wherein themolten slag-like composition comprises 60 to 90 wt.-% of magnesium oxideand/or calcium oxide and 10 to 40 wt.-% of silicon dioxide.

12. The process of any one of the preceding embodiments, wherein the PGMcollector alloy and the material capable of forming a slag-likecomposition when molten are melted in a weight ratio of 1:0.2 to 0.8 or1:0.2 to 0.6.

13. The process of any one of the preceding embodiments, wherein thetemperature of the converter contents is raised to 1200 to 1800° C.

14. The process of any one of the preceding embodiments, wherein thecontact between the oxidizing gas and the lower high-density molten massis made by passing or bubbling the gas through the lower high-densitymolten mass from the bottom of the converter and/or by means of a gaslance the exhaust of which being immersed into the lower high-densitymolten mass.

15. The process of any one of the preceding embodiments, wherein thecontact with the oxidizing gas takes 1 to 5 hours.

EXAMPLES Example 1

A premix of 500 kg of a PGM collector alloy comprising 47 wt.-% of iron,14.1 wt.-% of nickel, 8.1 wt.-% of silicon, 4.6 wt.-% of palladium, 3.2wt.-% of chromium, 2.5 wt.-% of titanium, 2.2 wt.-% of platinum, 1.8wt.-% of manganese, 0.6 wt.-% of rhodium and 0.9 wt.-% of copper, 123 kgof calcium oxide, 75 kg of silicon dioxide, 15 kg of sodium carbonateand 15 kg of borax was portionwise introduced into an already 1500° C.hot cylindrical natural gas-heated furnace and further heated to 1700°C.

After a melting time of 10 hours a two-phase system of a lowerhigh-density molten mass comprising the PGM collector alloy and an upperlow-density molten mass comprising a slag-like composition was formed.Oxygen was introduced into the lower high-density molten mass via aceramic pipe with an oxygen flow of 900 l/min. After 2.5 hours theoxygen introduction was stopped. The upper low-density molten mass waspoured into cast iron slag pots in order to cool down and solidify. Thelower high-density molten mass was then poured into graphite molds inorder to cool down and solidify. After solidification and cooling downto ambient temperature both materials were analyzed by XRF.

Examples 2 and 3

Example 1 was repeated with the difference that the oxygen introductiontook 2.75 hours (Example 2) or 3 hours (Example 3).

The results of the XRF analysis are compiled in Tables 1 and 2. Allvalues are in wt.-%, except the values for the PGM content in the slagwhich are in wt.-ppm:

TABLE 1 Composition of the solidified upper low-density mass (slag)Element Example 1 Example 2 Example 3 Fe 29 35 40 Ni 1 1 1 Total PGM 4947 44

TABLE 2 Composition of the solidified lower high-density mass (PGMenriched alloy) Element Example 1 Example 2 Example 3 PGM 27 28 34 Fe 2018 13 Ni 50 51 51

The invention claimed is:
 1. A process for the production of aPGM-enriched alloy comprising 0 to 60 wt.-% of iron and 20 to 99 wt.-%of one or more PGMs selected from the group consisting of platinum,palladium and rhodium, the process comprising the steps: (1) providing aPGM collector alloy comprising 30 to 95 wt.-% of iron, less than 1 wt.-%of sulfur and 2 to 15 wt.-% of one or more PGMs selected from the groupconsisting of platinum, palladium and rhodium, (2) providing a copper-and sulfur-free material capable of forming a slag-like composition whenmolten, wherein the molten slag-like composition comprises 40 to 90wt.-% of magnesium oxide and/or calcium oxide and 10 to 60 wt.-% ofsilicon dioxide, (3) melting the PGM collector alloy and the materialcapable of forming a slag-like composition when molten in a weight ratioof 1:0.2 to 1 within a converter until a multi- or two-phase system of alower, high-density molten mass comprising the molten PGM collectoralloy and one or more upper, low-density molten masses comprising themolten slag-like composition has formed, (4) contacting an oxidizing gascomprising 0 to 80 vol.-% of inert gas and 20 to 100 vol.-% of oxygenwith the lower, high-density molten mass obtained in step (3) until ithas been converted into a lower, high-density molten mass of thePGM-enriched alloy, (5) separating an upper, low-density molten slagformed in the course of step (4) from the lower, high-density moltenmass of the PGM-enriched alloy making use of the difference in density,(6) letting the molten masses separated from one another cool down andsolidify, and (7) collecting the solidified PGM-enriched alloy.
 2. Theprocess of claim 1, wherein the PGM-enriched alloy comprises or consistsof 0 to 45 wt.-% of iron and 30 to 99 wt.-% of the one or more PGMs, 0to 60 wt.-% of nickel, 0 to 5 wt.-% of copper, and 0 to 10 wt.-% of oneor more other elements.
 3. The process of claim 1, wherein thePGM-enriched alloy comprises or consists of 0 to 20 wt.-% of iron, 40 to90 wt.-% of the one or more PGMs, 0 to 60 wt.-% of nickel, 0 to 5 wt.-%of copper and 0 to 3 wt.-% of the one or more other elements.
 4. Theprocess of claim 1, wherein the PGM collector alloy provided in step (1)comprises 40 to 70 wt.-% of iron, 0 to 20 wt.-% of nickel, less than 1wt.-% of sulfur and 5 to 15 wt.-% of the one or more PGMs.
 5. Theprocess of claim 1, wherein the PGM collector alloy comprises no morethan 4 wt.-% of copper.
 6. The process of claim 1, wherein the PGMcollector alloy comprises or consists of: 30 to 95 wt.-% of iron, 0 to20 wt.-% of nickel, 0 to <1 wt.-% of sulfur, 2 to 15 wt.-% of the one ormore PGMs, 0 to 4 wt.-% of copper, and 0 to 30 wt.-% of one or moreother elements.
 7. The process of claim 1, wherein the PGM collectoralloy comprises or consists of: 40 to 70 wt.-% of iron, 0 to 15 wt.-% ofnickel, 0 to <1 wt.-% of sulfur, 5 to 15 wt.-% of the one or more PGMs,0 to 1 wt.-% of copper, and 0 to 20 wt.-% of one or more other elements.8. The process of claim 1, wherein the molten slag-like compositioncomprises or consists of: 40 to 90 wt.-% of magnesium oxide and/orcalcium oxide, 10 to 60 wt.-% of silicon dioxide, 0 to 20 wt.-% of ironoxide, 0 to 20 wt.-% of sodium oxide, 0 to 20 wt.-% of boron oxide, and0 to 2 wt.-% of aluminum oxide.
 9. The process of claim 1, wherein themolten slag-like composition comprises or consists of: 40 to 90 wt.-% ofmagnesium oxide and/or calcium oxide, 10 to 60 wt.-% of silicon dioxide,0 wt.-% of iron oxide, 0 to 10 wt.-% of sodium oxide, 0 to 10 wt.-% ofboron oxide, and 0 wt.-% of aluminum oxide.
 10. The process of claim 1,wherein the PGM collector alloy comprises 0 to 4 wt.-% of silicon andwherein the molten slag-like composition comprises 40 to 60 wt.-% ofmagnesium oxide and/or calcium oxide and 40 to 60 wt.-% of silicondioxide.
 11. The process of claim 1, wherein the PGM collector alloycomprises >4 to 15 wt.-% of silicon and wherein the molten slag-likecomposition comprises 60 to 90 wt.-% of magnesium oxide and/or calciumoxide and 10 to 40 wt.-% of silicon dioxide.
 12. The process of claim 1,wherein the PGM collector alloy and the material capable of forming aslag-like composition when molten are melted in a weight ratio of 1:0.2to 0.8 or 1:0.2 to 0.6.
 13. The process of claim 1, wherein thetemperature of the converter contents is raised to 1200 to 1800° C. 14.The process of claim 1, wherein the contact between the oxidizing gasand the lower high-density molten mass is made by passing or bubblingthe gas through the lower high-density molten mass from the bottom ofthe converter and/or by means of a gas lance the exhaust of which beingimmersed into the lower high-density molten mass.
 15. The process ofclaim 1, wherein the contact with the oxidizing gas takes 1 to 5 hours.